In recent years, a NAND type flash memory, which is an inexpensive large-capacity nonvolatile semiconductor memory, has been expanding its use and market as a storage memory such as a memory card or a solid state disk (SSD). The storage memory is required to be larger in capacity and lower in cost further and, for the purpose of the large capacity and the low cost, miniaturization of a processing size has been advanced.
When a NAND string length and a select gate transistor interval are made smaller to reduce the chip area and costs of the NAND type flash memory, an interval between the select gate transistors may be filled with gate sidewall films of the select gate transistors. In this case, a silicon nitride film is formed as a stopper film between the select gate transistors during a time when forming a contact to a semiconductor substrate, and the silicon nitride film may be increased in thickness or formed at a level higher than a due position on the semiconductor substrate. As a result, a failure may occur in that a contact hole may not be opened.